The present invention relates, in general, to arc fault detection and, more specifically, to arc fault detection in a direct current electrical system.
There are various conditions that may cause an arc fault. Corroded, worn or aged wiring or insulation, insufficient contact pressure, electrical stress from repeated overloading, etc., may result in an arc fault. These conditions may damage the insulation of the wiring and create excessive heating temperatures. In general, these conditions have been found to occur in applications where vibrations and relatively high temperatures are normally present. More specifically, vehicles (e.g. automobiles, airplanes, trucks, off-road equipment, etc.) and other moving or vibrating equipment provide a harsh environment for electronics and electrical systems (direct current (D.C.) or alternating current (A.C.)).
The development of electronics and electrically powered accessories has resulted in an increase in the use of electronics and electrical power in vehicles. Examples of electronics and electrically powered accessories used in vehicles include:
electronic fuel injection or fuel control;
electronic timing control;
electronic transmission shift control;
electronic HVAC control;
electronic lighting control;
electronic braking control (e.g. anti-lock braking, traction control, slip control, etc.);
power convenience accessories (e.g. power seats power windows, heated seats, personal lighting, heated steering wheels, power sun roof, power steering wheel tilt, power mirrors, tire inflation control, etc.);
electronic cruise control;
on-aboard navigation systems; and
air bags.
Many of the electronics and power accessories listed above are also used in aircraft and off-road vehicles (e.g. tractors, tracked vehicles, excavators, etc.). With hybrid and pure electric vehicles, the use and transmission of electrical power is multiples greater than with conventional vehicles due to the use of electricity to power the motors which propel the vehicles.
As a result of the substantial increase in use of electronics and electrical power accessories in vehicles, and the use of electric motors to propel vehicles, the potential for arc faults in the electrical systems of vehicles has also increased. As discussed above, such arcing can damage wiring and electronics or, cause unwanted heating. Thus, it would be desirable to provide a system for detecting and controlling arc faults in vehicle electrical systems.
Detection and control of arc faults is relatively complicated. For example, the occurrence of an arc fault in one branch circuit of a power distribution system of a vehicle may generate a false arc detection signal in another branch circuit. As a result, circuit breakers or interrupters in more than one branch circuit may erroneously trip. Relatively noisy loads within the vehicle, such as electric motors (engine fan, heater fan, power seat motors, etc.) can create high frequency disturbances, which may appear to be arc faults and cause unwanted circuit breaker tripping. Similarly, external high frequency disturbances within the vehicle""s operative environment also may appear to be arc faults and cause unwanted circuit tripping.
There are two types of arc faults that may occur in a vehicle. A first type is a high-energy arc that may be related to high current faults; a second type is a low current arc that may be related to the formation of a carbonized path between conductors. The first type may result from an inadvertent connection between a line conductor and neutral conductor or a line conductor and ground. The first type may draw current that is above the rated capacity of the circuit, arcing as the conductors are physically joined.
The other type of arc fault, the carbonization between electrical conductors, may be considered more problematic. Since the current in the arc may be limited to less than the trip rating of an associated circuit breaker or interrupter, such arcs may become persistent without observation and may result in certain conditions. Contact arcs may be caused by springs in switches that become worn which, in turn, may reduce the forces that hold electrical contacts together. As the electrical contacts heat and cool down, the conductors may touch and separate repeatedly, thereby possibly creating arcs known as xe2x80x9csputtering arcs.xe2x80x9d Such sputtering arcs can create carbonized paths resulting in persistent low current arcs in the electrical system.
Contact arcs or sputtering arcs may also be observed in contacts which are made from different materials. For example, aluminum wiring which contacts copper wiring may oxidize at the contact points. In this case a non-conductive layer may build up over time between the contact points and arcing may result.
In view of the potential for arc faults in vehicles, it would be desirable to provide vehicles with arc fault detection.
One embodiment of the present invention provides an arc detection circuit for detecting an arcing fault in a DC electrical system having a circuit protection system. The arc detection circuit comprises a superheterodyne circuit configured to monitor the DC electrical system. An oscillator circuit configured to generate an oscillator frequency with cycles between a low frequency and a high frequency is coupled to the superheterodyne circuit. A comparator circuit configured to eliminate background and spurious noise is coupled to the superheterodyne circuit and a reference voltage terminal. An arc timing monitor circuit configured to monitor time of the arcing fault based on a signal received from the comparator circuit. A compensating circuit configured to compensate for arcing drop outs when signal from the arc timing monitor circuit is received by the compensating circuit. An accumulating circuit configured to receive the signal from the compensating circuit and generate a further signal indicative of the arc fault if a predetermined time period is exceeded. And, a trip signal generation circuit configured to receive the further signal from the accumulating circuit and generate an arc signal to operate the circuit protection system. Another embodiment of the arc detection circuit includes filters coupled to the superheterodyne circuit. A further embodiment of the arc detection circuit provides each filter is configured to operate at a frequency of 10.7 mega Hz.
Another embodiment of the present invention provides a method for detecting an arcing fault in a DC electrical system having a circuit protection system. The method of arc detection comprises the steps of monitoring the DC electrical system with a superheterodyne circuit. Generating an oscillator frequency which cycles between a low frequency and a high frequency, with an oscillator circuit coupled to the superheterodyne circuit. Eliminating background and spurious noise with a comparator circuit coupled to the superheterodyne circuit and a reference voltage terminal. Monitoring time of the arcing fault based on a signal from the comparator circuit with an arc timing monitor circuit. Compensating for arcing drop-outs based on a signal from the arc timing monitor circuit with a compensating circuit. Generating a further signal indicative of the arc fault if a predetermined time period is exceeded, with an accumulating circuit based on the signal from the compensating circuit. And, generating an arc signal to operate the circuit protection system with a trip signal generation circuit based on the further signal from the accumulating circuit.
Another embodiment of the present invention provides an arc detection circuit for detecting an arcing fault in a DC electrical system having a circuit protection system. The arc detection system comprising a means for monitoring the DC electrical system. A means for generating an oscillator frequency which cycles between a low frequency and a high frequency with the means for generating coupled to the means for monitoring. A means for eliminating background and spurious noise coupled to the means for monitoring and a reference voltage terminal. The means for monitoring time of the arcing fault based on a signal from the means for eliminating. A means for compensating for arcing drop-outs based on a signal from the means for monitoring time. A means for generating a further signal indicative of the arc fault if a predetermined time period is exceeded, based on the signal from the means for compensating. And, a means for generating an arc signal to operate the circuit protection system, based on the further signal from the means for generating a further signal. An additional embodiment provides the means for monitoring to be coupled to the DC electrical system by one of an electromagnetically coupler or a mechanical coupler.